Just out of curiosity

Anywhere and everywhere
Figurines/nic-nacs; balloons; any kind of art; art books; fabric; nature;
Haven't you ever walked through a store or see a picture in a book and say "Hey, that would make a cute cake!" ?

And, of course, seeing other's cakes. Take elements from this one, ...another element from that one and some thoughts of your own to come up with a new, different creation.

I agree with kakeladi. Incorporate what you like from other cakes into your own cake. A fence, a bird, color, etc. The list is endless.

Scrapbooking paper is great inspiration!

I agree with the above posters - you can find inspiration anywhere! One of my daughters has a really cute summer dress that I think would look great as a cake.

Here's an example of a cookie I made after seeing a pretty wedding album:

Cookie
http://letsgetcaking.blogspot.com/2010/10/creative-pumpkins.html

Album
http://factorydirectcraft.com/pimages/20070330134240-417206/cinderella_carriage_wedding_guest_registry_sign_in_book.jpg

Fabric, textiles. I also put any kind of search word I "like" into Google Images, such as Paris, India, tulips, dutch design, scandinavian design, etc. Then I sometimes limit it to line drawings or clip art.